Until recently, unilateral infantile cataracts were considered to be untreatable because lack of form or pattern vision during the early postnatal months inevitably resulted in profound, irreversible amblyopia from unbalanced visual inputs. However, in recent years a number of laboratory and clinical reports have indicated that it might be possible to maintain functional vision in these eyes by prompt surgical removal of the cataract, correction of the resulting aphakia, and aggressive occlusion of the opposite eye. We have developed a monkey model with which we can study these treatments. We conduct a lensectomy shortly after birth on deeply anesthetized monkeys using sterile procedures similar to those that would be used with human babies. Then we fit the infant monkeys with extended-wear contact lenses that are manufactured in our own laboratory specifically for infant monkey eyes. Some contact lenses provide an optical correction to the eye, allowing that eye to see more clearly. Other lenses defocus, diffuse, or occlude light, thus forcing the animal to use its opposite eye. Studies conducted in our laboratories have determined that continuous occlusion for long periods is always detrimental to visual function in the occluded eye and often leads to ocular misalignment. Therefore, our current research focus is on treatments that involve either minimal occlusion or no occlusion. Complete ophthalmic examinations are conducted on our animals at regular intervals to document the clinical status of our treatment groups. Behavioral outcome measures include assessments of visual functions including acuity, contrast sensitivity, spatial localization, spatial phase sensitivity, and extent of the visual fields. Visually evoked potentials (VEPs) will also be measured periodically and related to the behavior results. At the end of the rearing period, neuroanatomical studies will be conducted so that each treatment paradigm can be evaluated in terms of the correlations between visual function and central nervous system changes. The results of these studies will provide direct information about deficits in the central visual pathways that result from infantile aphakia in monkeys. These results can also be extrapolated to human infants with aphakic amblyopia because of the close similarities of macaque monkey and human visual systems. Therefore, our studies have direct clinical relevance for devising treatments of human infants who are born with unilateral cataracts.